The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A relatively new type of automatic transmission is referred to as a dual countershaft or dual clutch transmission (DCT). In a dual countershaft transmission, a pair of countershafts or lay shafts are disposed on opposite sides of the common axis of the input shaft and output shaft and in the same plane. Typical dual countershaft transmissions are split torque devices in which both countershafts carry load. This, as noted, requires the shafts to be in the same plane.
In other dual countershaft transmission configurations, only one countershaft carries load at a time. The countershafts can be located anywhere around the output shaft providing they do not interfere and provided there is room for the reverse idler. The countershafts are mutually exclusively driven by engagement of one of a pair of range clutches operably disposed between the input shaft and a respective one of the countershafts. A plurality of gears are secured to and rotate with the output shaft and each output shaft gear is in constant mesh with a one of a plurality of gears freely rotatably supported on the countershafts. Synchronizers and clutches selectively engage a single gear with its associated countershaft and the countershaft range clutch is then engaged to transmit torque from the input shaft to the output shaft.
In order to provide smooth and responsive gear shifts, the synchronizer must quickly adjust the speed of the countershaft to that of the selected gear so that a positive, e.g., dog, clutch can be fully engaged before the range clutch is engaged. If the range clutch engages before the countershaft speed is fully synchronized and the positive clutch is engaged, the engine to drive wheel connection would be lost and synchronizer damage would occur. Accordingly, the synchronizer must act quickly to facilitate engagement of the positive clutch. One of the factors affecting synchronizing time is the mass or inertia of the components to be synchronized.
The mass of the countershaft and that of all components rotating with it has been the object of much attention. For example, the countershaft is hollow in order to both reduce its mass and locate the metal that remains in a relatively thin wall, where it can carry the maximum load and torque. The benefits of this approach suggest that further effort to reduce the mass of the countershaft and its associated components would be worthwhile and this invention is the result of such effort.